He sang with a male quartet called the Cadets on several Chicago-based radio shows, including "The Breakfast Club With Don MacNeil." He later formed the Jack Halloran Quartet, which appeared on the television programs "Dave Garroway at Large" and "The Pat Buttram Show." Relocating to Hollywood, Halloran became a choral director for films, records and television, working with such entertainers as Roy Rogers, Pat Boone, Ray Charles, Frank Sinatra and Dean Martin. He landed the job as choral director and arranger on The Dean Martin Show while working with the singer on his recording of "Volare." Halloran also organized the Jack Halloran Singers, which performed throughout Southern California. Halloran directed the orchestra and chorus for Bing Crosby's 1959 LP Join Bing and Sing Along. He directed the chorus for Bing's 1962 LPs Great Standards and I Wish You a Merry Christmas and Bing's 1970 LP A Time to Be Jolly. He was also a member of the Ray Conniff Singers, appearing on such albums as Speak to Me of Love (Columbia, 1963).
Witness (1986) was first released in an a cappella setting for 8-part mixed voices, and within months had sold over 30,000 copies. The following year it topped 50,000 and continued to climb. Today it remains a top seller and an industry standard. Veteran arranger Dick Bolks has revoiced and edited Halloran's setting into an SATB edition with optional accompaniment.